1. Field of the Invention
The present invention relates to an ion source for a quadrupole mass spectrometer.
2. Description of the Prior Art
A source of this type is disclosed in U.S. Pat. No. 4,006,894, the teachings of which are considered here by way of reference. The source comprises, from the upstream end to the downstream end in the axis of the quadrupole, an ionization chamber with heated filament and electrostatic field associated with an electron-optical system provided with an electron convergence device.
By reason of the symmetry of revolution imposed by the quadrupole filter, known ion sources for quadrupoles are so designed as to produce a circular beam directly. To this end, manufacturers employ an ion chamber having an exit in the form of a circular orifice followed by a focusing electron lens, the complete assembly being placed in the axis of the quadrupole filter.
In practice, the limitations in size of the circular orifice impose a restriction on the maximum sensitivity of this device.
The aim of the invention is to propose a novel configuration of an ion source for a quadrupole spectrometer which permits a considerable improvement in sensitivity.